Many pesticides require the addition of an adjuvant to the spray mixture to provide wetting and spreading on foliar surfaces. Often that adjuvant is a surfactant, which can perform a variety of functions, such as increasing spray droplet retention on difficult to wet leaf surfaces, or to provide penetration of the herbicide into the plant cuticle. These adjuvants are either provided as a component in an adjuvant formulation or used as an additive in herbicide formulations.
Gaskin, et al., (Pestic. Sci. 1993, 38, 185-192) demonstrated that some trisiloxane ethoxylates (TSE), such as Silwet L-77.RTM. surfactant (available from OSi Specialties, Inc. of Danbury, Conn.), can antagonize cuticular penetration of glyphosate herbicide into grasses, when compared to the herbicide alone. The term antagonism is used to indicate that the treatment of herbicide plus adjuvant is less effective than the comparative herbicide treatment.
This antagonism can be mitigated if the number of ethylene oxide (EO) units contained in the TSE is increased to 17 or more; however, superspreading of the TSE is dramatically reduced once the degree of ethoxylation exceeds about 12 EO and TSE's containing the higher EO adducts show spreading properties similar to conventional nonsilicone surfactants.
Sandbrink, et al., (Pest. Sci. 1993, 38, 272-273) published that a TSE antagonized glyphosate performance relative to glyphosate alone in the control of Panicum maximum Jacq.
Snow, S. A. et. al., Langmuir, 1993, 9, 424-30, discusses the physical properties and synthesis of novel cationic siloxane surfactants. These siloxanes are based on the reaction of a chloropropyl modified trisiloxane with an alkanolamine, such as N-methylethanolamine, which was further reacted with a halide to make a quaternary surfactant.
Petroff, et al., (EP 92116658) describes the use of cationic, quaternary trisiloxanes to enhance the efficacy of glyphosate on velvetleaf, a broadleaf weed. Henning, et al., (DE4318537) describes cationic siloxanyl modified polyhydroxy hydrocarbon or carbohydrate for use with plant protection agents. These compounds are derived from a saccharide containing 1 to 10 pentose and/or hexose units, modified with a quaternary ammonium group, and a siloxane moiety.